Re: [net-next v2] pfcp: avoid copy warning by simplifing code

[Michal Swiatkowski <michal.swiatkowski@linux.intel.com>]

On Mon, Apr 08, 2024 at 09:18:29AM +0100, Simon Horman wrote:
> On Fri, Apr 05, 2024 at 08:36:05AM +0200, Michal Swiatkowski wrote:
> > >From Arnd comments:
> > "The memcpy() in the ip_tunnel_info_opts_set() causes
> > a string.h fortification warning, with at least gcc-13:
> > 
> >     In function 'fortify_memcpy_chk',
> >         inlined from 'ip_tunnel_info_opts_set' at include/net/ip_tunnels.h:619:3,
> >         inlined from 'pfcp_encap_recv' at drivers/net/pfcp.c:84:2:
> >     include/linux/fortify-string.h:553:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
> >       553 |                         __write_overflow_field(p_size_field, size);"
> > 
> > It is a false-positivie caused by ambiguity of the union.
> > 
> > However, as Arnd noticed, copying here is unescessary. The code can be
> > simplified to avoid calling ip_tunnel_info_opts_set(), which is doing
> > copying, setting flags and options_len.
> > 
> > Set correct flags and options_len directly on tun_info.
> > 
> > Fixes: 6dd514f48110 ("pfcp: always set pfcp metadata")
> > Reported-by: Arnd Bergmann <arnd@arndb.de>
> > Closes: https://lore.kernel.org/netdev/701f8f93-f5fb-408b-822a-37a1d5c424ba@app.fastmail.com/
> > Acked-by: Arnd Bergmann <arnd@arndb.de>
> > Signed-off-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
> 
> I agree that it's nice to avoid a copy.
> But I do wonder where else this pattern may exist.
> And if it might be worth introducing a helper for it.

Right, the same is done in vxlan, ip_gre and ip6_gre at least. I will
send v3 with helper.

Thanks,
Michal

> 
> Regardless, this looks good to me.
> 
> Reviewed-by: Simon Horman <horms@kernel.org>
> 
> ...